Thermal cycling in support of Polymerase Chain Reaction (PCR) is a ubiquitous technology found in over 90% of molecular biology laboratories worldwide.
Amplifying DNA (Deoxyribose Nucleic Acid) using the PCR process, involves cycling a specially constituted liquid reaction mixture through several different temperature incubation periods. The reaction mixture is comprised of various components including the DNA to be amplified and at least two primers sufficiently complementary to the sample DNA to be able to create extension products of the DNA being amplified. A key to PCR is the concept of thermal cycling: alternating steps of denaturing DNA, annealing short primers to the resulting single strands, and extending those primers to make new copies of double-stranded DNA. In thermal cycling the PCR reaction mixture is repeatedly cycled from high temperatures of around 95° C. for denaturing the DNA, to lower temperatures of approximately 50° C. to 70° C. for primer annealing and extension.
In some previous PCR instruments, sample tubes are inserted into sample wells on a metal block. To perform the PCR process, the temperature of the metal block is cycled according to prescribed temperatures and times specified by the user in a PCR protocol. The cycling is controlled by a computer and associated electronics. As the metal block changes temperature, the samples in the various tubes experience similar temperature changes. However, in these previous instruments the overall size or footprint is frequently large and therefore occupy significant space on a laboratory bench. In many laboratories open bench space is frequently hard to find. In some previous instruments a reason for the relatively large footprint can be due to the dimensions of the various components and subassemblies required to cycle samples to perform the PCR process.
Components that contribute to the overall size of the instrument are the printed circuit boards (PCBs) used to provide the thermal control of the metal block and ultimately of the sample. In some previous instruments two printed circuit boards are included. One of the PCBs sometimes referred to as an Interface Board, is positioned around the perimeter of the thermoelectric devices and can be used to provide electrical connections to the thermoelectric devices, thermal sensors and other necessary electronics. Another PCB, sometimes referred to as an Amplifier Board, can be used to provide electrical currents to the thermoelectric devices in a controlled manner dependent on the desired or setpoint temperature of the metal block and the temperature of the metal block or sample detected by a thermal sensor. Thermoelectric devices utilize the Peltier effect to pump heat from one side of the device to another. In operation, a thermoelectric device is provided with an electrical DC current. Current flows through the TEC and results in one surface becoming hot while the opposing surface becomes cold. By reversing the direction of the current the surface that was hot becomes cold and the surface that was cold becomes hot.
Frequently thermoelectric devices do not perform well in environments that are moist. Moisture contributes to corrosion of electrical connections within the device. The corrosion increases the resistance of the connections and eventually results in a premature failure of the device, and low reliability of the instrument.
In some previous instruments the number of thermoelectric devices and the size of each thermoelectric device can be large. In some previous instruments the number of thermoelectric devices can be 1, 2, 4, 6, 8 or any other number suitable for the application. An Interface Board providing the necessary electrical connections, therefore, can be substantial. Additionally the PCB can be positioned around the perimeter of the TECs, further contributing to the overall size of the instrument.
In some previous instruments thermoelectric devices require significant electrical current to power the thermoelectric devices. Depending on the instrument, the required current may be greater than 10 amperes. Providing currents of this magnitude frequently require the use of large electrical components, for example inductors, to provide the necessary current. The size of the electrical components impacts the size of the Amplifier Board and further impacts the size of the instrument.
Providing small, scalable, reliable and affordable high performance instruments with a small footprint therefore, becomes desirable to scientists around the world.